1. The Field of The Invention
The present embodiment concerns a system and process for measuring the color of a material such as a sheet of paper.
2. State of the Art
During the production of many materials, the color of the material must be measured and controlled. For example, during the production of liquids such as paint or during the production of sheet materials such as plastics or paper, certain pigments are added to a base material to provide color, and the amount of each pigment must be carefully controlled to insure that the color is within specified standards.
U. S. Pat. No. 3,936,189 to De Remigis teaches a system for continuously monitoring the color of a moving sheet of paper. According to the patent an optical head includes a light integrating sphere for directing light from a source onto the web, and a plurality of sensing units are mounted in the upper portion of the sphere. On the opposite side of the sheet from the sensing unit is mounted an optical shoe providing black and white backgrounds. The black and white backgrounds are arranged to permit one or the other to be used to back the sheet during measurement of the color. The white background is produced by applying a white stripe to a quartz shoe.
We have found that systems such as those described in the patent using a white background in the form of paint or similar material can be inadequate for backing certain papers. That is, the measured color of a sheet of paper backed with a white standard such as white paint can vary significantly from the actual color of the sheet of paper.